POTASSIUM CURRENTS OF PEAR-SHAPED HAIR-CELLS IN RELATION TO THEIR LOCATION IN FROG CRISTA-AMPULLARIS

VOLTAGE-DEPENDENT K+ currents in pear-shaped hair cells of the frog cr ista ampullaris were investigated in thin slice preparations using the whole-cell variant of the patch-clamp technique. Microscopy observati on revealed that pear-shaped cells are located in intermediate and per ipheral regions of the crista, whereas they are absent in the central region. Voltage-clamp recordings in cells from the peripheral regions revealed that the total outward K+ current could be separated pharmaco logically into three distinct components: a A-type K+ current (I-A); a n inactivating calcium-activated K+ current (I-K(Ca)) and a delayed re ctifier K+ current (I-K) I-K and I-K(Ca) exhibited similar magnitude a nd accounted for most of the membrane cell conductance. The same exper imental protocol applied to cells from the intermediate regions showed the presence of a large and sustained I-K(Ca) which represented 95% o f the total outward current. In this region I-A was absent. The presen t results demonstrated that pear-shaped hair cells located in two disc rete regions of frog crista ampullaris exhibit a different complement of voltage-dependent conductances, suggesting that they can play a dif ferent role in processing the natural stimulus.